Compositions containing highly viscous polyisocyanates

ABSTRACT

The invention provides a composition for producing surface coatings combining improved hardness, scratch resistance and acid resistance with good reflow behavior, a process for preparing such a surface coating, and for the use of polyisocyanatoisocyanurates having a functionality of more than 3.5 and a viscosity at 23° C. of more than 3500 to produce surface coatings.

The invention relates to a composition comprising at least oneisocyanate which is essentially free from allophanate groups and has anaverage functionality or more than 3.5 and a viscosity of from 4000 to50000 mPas at from 20° C. to 50° C. and at least one compound havingmore than at least 5 functional groups which are reactive towardisocyanates with formation of urea or urethane and leading topolyurethanes combining improved hardness, scratch resistance and acidresistance with good reflow behavior. The invention further relates to aprocess for preparing such a composition and to the use of certainpolyisocyanatoisocyanurates for preparing such compositions.

With polyurethane coating materials, especially those intended for usein the automotive or furniture sectors, particular value is generallyplaced on the resistance of such coatings to different environmentalinfluences. Examples of criteria frequently employed to evaluate suchcoatings are their hardness, the scratch and acid resistance, and alsothe reflow behavior.

The reflow behavior is the ability of a cured surface coating (finish)to compensate for relatively small damage sites (in the μm range) whichhave come about by scratching or impact on the finish by cold flow ofthe finish into the damage site.

To improve the scratch resistance, use has frequently been made in thepast of oligomeric polyisocyanatoisocyanurates based on hexamethylenediisocyanate (HDI) as the isocyanate component. The polyurethanefinishes produced therefrom are generally soft and therefore possessgood reflow behavior. A disadvantage of such finishes, however, is theirinadequate acid resistance.

Hard and acid resistant polyurethane finishes are generally obtainedwhen the polyisocyanate component used comprises, for example, IPDI orthe oligomeric polyisocyanatoisocyanurates of IPDI. However, the scratchresistance and reflow behavior or such products is generally inadequate.A further disadvantage of the IPDI based products in respect of a largescale use for the production of mass products is their high price incomparison to that of HDI.

It is an object of the present invention to provide a composition whichcan be used as a polyurethane coating material and which, after curing,gives surface coatings combining good hardness, scratch resistance andacid resistance with good reflow behavior.

CA-A 2,163 591 relates to polyisocyanate mixtures containing allophanateand isocyanurate groups. Such isocyanate compounds are prepared, forexample, by adding a certain amount of a monoalcohol having a molecularweight of up to about 2500 g/mol to a suitable amount of hexamethylenediisocyanate. Subsequent heat treatment of such a mixture produces thecorresponding polyisocyanates containing allophanate groups. Thereaction with monoalcohols, however, leads to polyisocyanates whoseisocyanate group content per molecule (based on the molecular weight) islower than the isocyanate group content of polyisocyanates preparedwithout adding monoalcohols. Owing to this reduced number of isocyanategroups per molecule, the functionality required for network formation isreduced, resulting in a lower network density with reductions in thedesired properties. Moreover, the document gives no information on thereflow behavior of surface coatings produced with isocyanates containingallophanate groups, nor their acid resistance.

U.S. Pat. No. 4,419,513 relates to mixed isocyanurates obtainable bymixed trimerization of HDI and IPDI. It is stated that the mixed trimersdescribed have desirable properties in respect of hardness andelasticity. A disadvantageous effect with these mixed trimers is that,owing to the IPDI fraction, the isocyanate group content (based on themolecular weight) is lower than in the case of straight HDI trimers,which brings economic disadvantages.

U.S. Pat. No. 4,454,317 mentions polyisocyanatoisocyanurates obtainable,for example, by trimerizing HDI. Described by way of example is an HDItrimer having an NCO content of 20.8% and a viscosity of 14 Pas at roomtemperature. The document says nothing about the possibility ofpreparing polyurethanes having improved chemical resistance by combiningsuch polyisocyanatoisocyanurates with appropriate polyols.

EP-A 0 646 608 relates to polyisocyanates obtainable by cyclictrimerization of at least one aliphatic or alicyclic diisocyanate eitherfollowing its reaction with a polyfunctional alcohol or by trimerizationin the presence of such an alcohol. Although such isocyanates have highviscosities, the fraction of polyfunctional alcohol in thepolyisocyanate molecule prepared produces a fall in the weight fractionof isocyanate groups per molecule. When the polyisocyanate is used, thisnecessitates the employment of a larger amount of isocyanate, which iseconomically undesirable.

U.S. Pat. No. 4,801,675 relates to polyisocyanatoisocyanurates having anisocyanate content of from 10 to 30% by weight and to their reactionwith polyols which have an average functionality of from 1.8 to 5.

As stated, it is an object of the present invention to provide acomposition which possesses excellent hardness, scratch resistance andacid resistance in conjunction with good reflow behavior.

We have found that this object is achieved by a composition whichcomprises at least one polyisocyanatoisocyanurate which is essentiallyfree from allophanate groups and has an average NCO functionality ofmore than 3.5 and a viscosity of more than 4000 mPas up to 50000 mPas atfrom 20° C. to 50° C. and at least one compound having on average morethan 5 functional groups which are reactive toward isocyanates withformation of urea or urethane and which leads to surface coatings whichpossess excellent hardness, scratch resistance and especially acidresistance coupled with good reflow behavior.

The invention accordingly provides a composition comprising components Aand B, comprising

a) as component A at least one polyisocyanatoisocyanurate which isessentially free from allophanate groups and has an average NCOfunctionality of more than 3.5 and a viscosity of more than 4000 mPas upto 50000 mPas at from 20° C. to 50° C., measured with a rotationalviscometer in accordance with DIN 53019, and

b) as component B at least one compound containing on average more than5 functional groups which are reactive toward isocyanates with formationof urea, urethane, thiourethane or amide.

The term “essentially free from allophanate groups” refers to compoundswhose fraction of allophanate groups is less than 10% in relation toisocyanurate groups.

A polyisocyanatoisocyanurate is a compound possessing at least oneisocyanurate ring and at least 2, preferably at least 3, isocyanategroups. The number of isocyanurate rings and the NCO functionality arealways calculated as an average of the overall mixture of compounds usedas component A. Since the trimerization of diisocyanates generally leadsnot to pure products but rather to compounds having different degrees ofoligomerization, the functionality of the resulting compounds can onlybe stated as an average value.

It is known that isocyanates may be converted into isocyanurates withthe aid of catalysts.

The literature describes numerous catalysts for the cyclization ofisocyanates to isocyanurates. Examples of such catalysts are strongbases such as quaternary ammonium hydroxides, e.g.,benzyltrimethylammonium hydroxide, alkali metal hydroxides, e.g., sodiumor potassium hydroxide, alkali metal alkoxides, e.g., sodium methoxideor potassium isopropoxide, trialkylphosphines, e.g., triethylphosphine,alkylaminoalkylphenols, e.g., 2,4,6-tris(dimethylaminomethyl)phenol, 3-or 4-substituted pyridines or mixtures thereof, e.g., 3- or4-methylpyridine, organometallic salts, e.g.,tetrakis(hydroxyethyl)sodium borate, Friedel-Crafts catalysts, e.g.,aluminum chloride, iron(III) chloride, boron trifluoride and zincchloride, and alkali metal salts of weak organic acids andnitrophenoxides, e.g., potassium octoate, potassium 2-ethylhexoate,potassium benzoate, sodium picrate and potassium phthalimide. Likewisesuitable are the quaternary N-(hydroxyalkyl)ammonium salts of organicacids, as described, for example, in U.S. Pat. No. 4,454,317.

In order to polymerize organic polyisocyanates to polymerizationproducts having an isocyanurate structure and free NCO groups it isnecessary to terminate the formation of isocyanurate after the desireddegree of polymerization has been reached. This is generally achieved bydecomposing or neutralizing the catalysts. If, for example, a basiccatalyst is used, the reaction may be terminated by adding an amount ofan acid, e.g., p-toluenesulfonic acid, or an acid chloride, e.g.,benzoyl chloride, which is at least equivalent to the amount ofcatalyst. If a heat sensitive catalyst is used, a quaternary ammoniumhydroxide, for example, the reaction may be interrupted without adding acatalyst poison by heating the reaction mixture to a temperature atwhich the catalyst is destroyed. A further possibility is to use acatalyst which has been applied to a support material. Following thereaction, such a catalyst may be removed from the reaction mixture bycustomary solid/liquid separation methods: for example, by filtration orcentrifugation.

Examples of suitable quaternary ammonium hydroxides are tetramethyl-,tetraethyl-, trimethylstearyl-, dimethyl-, ethyl- or cyclohexylammoniumhydroxide;N,N,N-trimethyl-N-(2-hydroxyethyl)-,N,N,N-trimethyl-N-(2-hydroxypropyl)-,N,N,N-trimethyl-N-(2-hydroxybutyl)-,N,N-dimethyl-N-dodecyl-N-(2-hydroxyethyl)- orN-(2-hydroxyethyl)-N,N-dimethyl-N-(2,2-di-hydroxymethyl-butyl)ammoniumhydroxide; N-methyl-2-hydroxyethylmorpholinium hydroxide;N-methyl-N-(2-hydroxypropyl)pyrrolidinium hydroxide;N-dodecyltris-N-(2-hydroxyethyl)ammonium hydroxide;tetra(2-hydroxyethyl)ammonium hydroxide; and the salts of theabove-mentioned ammonium ions with anions other than the stated OH⁻ions, and also mixtures of two or more of the abovementioned compounds.Suitable counterions include, for example, the anions of organiccarboxylic acids having 1 to about 20 carbon atoms. Examples of theseare the anions of formic, acetic, propanoic, butanoic, pentanoic,hexanoic, heptanoic, caproic, caprylic, capric, lauric, myristic,palmitic or stearic acid. In one preferred embodiment of the presentinvention, the anion of 2-ethylhexanoic acid is used as the counterion.

The trimerization catalysts are generally used in an amount of from0.0001 to about 5% by weight, in particular from about 0.001 to about 2%by weight, based on the diisocyanates used. In one preferred embodiment,the catalysts may be used, for example, in an amount of from about 0.005to about 1.5, in particular in an amount of from about 0.01 to about 1%by weight.

As isocyanates it is possible in principle to use all diisocyanateswhose trimerization leads to products which have the properties, interms of functionality and viscosity, that are required in accordancewith the invention. Such isocyanates comprise, in particular,1,2-ethylene diisocyanate, 1,4-tetramethylene diisocyanate,1,6-hexamethylene diisocyanate (HDI), 2,2,4- or2,4,4-trimethyl-1,6-hexamethylene diisocyanate (TMHDI),1,9-diisocyanato-5-methylnonane, 1,8-diisocyanato-2,4-dimethyloctane,1,12-dodecane diisocyanate, ω,ω′-diisocyanatodipropyl ether, cyclobutene1,3-diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate,3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophoronediisocyanate, IPDI), 1,3- and 1,4-diisocyanatomethylcyclohexane, 2,4-and 2,6-hexahydrotolylene diisocyanate, perhydro-2,2′-, -2,4′- and-4,4′-diphenylmethane diisocyanate,4,4′-diisocyanato-3,3′,5,5′-tetramethyldicyclohexylmethane orω,ω′-diisocyanato-1,4-diethylbenzene.

Preference, however, is given to the use of linear or branched aliphaticor cycloaliphatic diisocyanates, especially linear aliphaticdiisocyanates. Particular preference is given to apolyisocyanatoisocyanurate as obtainable by trimerizing HDI.

The isocyanate compounds which may be used as component A preferablyhave a functionality of from 4.0 to 7.0, in particular from 4.2 to 6.5.

To prepare the polyisocyanatoisocyanurates which may be used ascomponent A, an appropriate catalyst is added to the abovementioneddiisocyanates or mixtures of two or more of the abovementioneddiisocyanates at from about 0° C. to about 150° C. Subsequently, theymay be reacted at these temperatures, preferably at from 10° C. to 100°C., in particular from about 20° C. to about 80° C., until the desiredNCO number is reached. The reaction time required is normally from about0.1 to about 16 hours, for example, from about 0.25 to about 4 hours.The reaction may be conducted in the absence or in the presence oforganic solvents. Suitable solvents are solvents which are inert towardisocyanates. Examples of these are methylene chloride, chloroform,chlorobenzene, acetone, methyl ethyl ketone, ethyl acetate, butylacetate, tetrahydrofuran, dioxane, toluene or xylene or mixtures of twoor more thereof. On reaching the desired NCO number, the reaction isterminated by a catalyst deactivating additive or by otherwisedeactivating the catalyst: by heating, for example.

Suitable deactivators (catalyst poison) include strong acids or carbonylhalides. In this context mention may be made, for example, of acids suchas phosphoric acid, hydrochloric acid or p-toluenesulfonic acid and ofcarbonyl halides such as acetyl chloride, benzoyl chloride ortoluenesulfonyl chloride, or mixtures of two or more thereof. Ingeneral, the reaction is effectively ended by adding from about 1 toabout 20 acid or acid halide equivalents per equivalent of catalyst.

Following the termination of the reaction, the unreacted monomericdiisocyanates and, if appropriate, the solvents are normally removedunder gentle conditions. This may be achieved, for example, by means ofvacuum distillation in appropriate evaporators or by means of extractionwith appropriate solvents in which only the monomeric diisocyanates, butnot the trimeric or polymeric polyisocyanates or mixtures thereof, aresoluble: for example, using aliphatic or cycloaliphatic hydrocarbons.

The residual monomer content of the polyisocyanatopolyisocyanurates usedas component A is preferably less than about 2% by weight, in particularless than about 1% by weight. In one particularly preferred embodimentof the present invention, the polyisocyanatopolyisocyanurates used ascomponent A have a residual monomer content of less than about 0.5% byweight.

As component B, the compositions of the invention comprise at least onecompound having on average more than 5 functional groups which arereactive toward isocyanates with formation of urea or urethane. Theaverage amount of functional groups which are reactive towardisocyanates with formation of urea or urethane is based on the entiretyof the compounds used as component B.

Accordingly, component B may, for example, consist exclusively ofcompounds of which each individual molecule has the requiredfunctionality. It is also possible as component B, however, to use amixture of compounds comprising compounds or a mixture of two or morecompounds whose molecules contain less than 5 groups which are reactivetoward isocyanates with formation of urea or urethane. All that isnecessary in such a case is to ensure that the entirety of the compoundspresent in component B complies with the required average functionality.

Accordingly, component B may also comprise compounds having afunctionality with respect to isocyanates of two, three, four or five.Examples of compounds regarded as functional with respect to isocyanatesare those having functional groups selected from the group consisting of—OH, —SH, —R—NH or —COOH or a mixture of two or more thereof, R beinghydrogen or a linear or branched, saturated or unsaturated alkyl radicalhaving 1 to about 12 carbon atoms or a linear or branched, saturated orunsaturated cycloalkyl radical having 3 to about 12 carbon atoms.

In one preferred embodiment of the invention, component B comprisescompounds whose functional groups are R—NH or OH groups or both, R beingas defined above. It is particularly preferred, however, if thecompounds used as component B have OH groups as their isocyanatereactive functional groups. In the text below, such compounds arereferred to as polyols.

In one preferred embodiment of the invention, polyols are used ascomponent B which have a molecular weight (M_(n)) of from about 62 toabout 500000, in particular from about 300 to about 40000, and withparticular preference from about 1000 to about 25000 g/mol.

Examples of compounds of low molecular mass are ethylene glycol,propylene glycol, butylene glycol, propanediol, pentanediol, hexanediol,heptanediol, octanediol and the higher homologs thereof, glycerol,trimethylolpropane, triethylolpropane, pentaerythritol, pentoses orhexoses such as glucose or sorbitol and also oligosaccharides orpolysaccharides such as sucrose or maltose, or mixtures of two or moreof said compounds.

Also suitable for use in component B are reaction products of theabovementioned compounds with themselves or reaction products of amixture of two or more of the abovementioned compounds, for example,polyethylene glycol or polypropylene glycol having a degree ofpolymerization of from two to about 1000. Likewise suitable are thereaction products of the abovementioned compounds with an alkylene oxidehaving two to about 10 carbon atoms or with a mixture of two or moresuch alkylene oxides, for example, with ethylene oxide, propylene oxideor butylene oxide or with a mixture of two or more thereof.

Further compounds suitable and necessary for use in component B arecompounds having at least on average 5 or more functional groups fromthe group consisting of —OH, —SH, —R—NH or —COOH or a mixture of two ormore thereof. R is as defined above. The compounds which may be used incomponent B preferably comprise compounds having at least predominantlyOH groups as functional groups which are reactive toward isocyanates.

Suitable in the context of the present invention for use as component B,for example, are polyols based on acrylic or methacrylic acid. Such(meth)acrylate polyols comprise, for example, those polyols obtainableby copolymerizing polymerizable (meth)acrylic monomers having one ormore isocyanate reactive hydrogen atoms in one molecule. Examples ofsuch (meth)acrylic monomers having one or more isocyanate reactivehydrogen atoms are 2-hydroxyethyl(meth)acrylate,2-hydroxydiethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, or2-hydroxybutyl(meth)acrylate. Also suitable are (meth)acrylic estershaving two or more isocyanate reactive groups, as obtainable by reacting(meth)acrylic acid with a substoichiometric amount of compounds havingtwo or more isocyanate reactive groups. Examples of these are the(meth)acrylic monoesters or diesters of glycerol, trimethylolpropane,triethylolpropane or pentaerythritol, of saccharides such as glucose,mannitol or sorbitol, or of oligosaccharides or polysaccharides such assucrose or maltose, and also mixtures of two or more of said compounds.

Examples of suitable comonomers are methyl(meth)acrylate,isopropyl(meth)acrylate, n-butyl(meth)acrylate,2-ethylhexyl(meth)acrylate, isobutyl(meth)acrylate,n-hexyl(meth)acrylate, cyclohexyl(meth)acrylate, lauryl(meth)acrylate orglycidyl(meth)acrylate.

If desired, further monomers may be present at the polymerization,examples being unsaturated carboxylic acids such as acrylic acid,methacrylic acid, maleic acid or itaconic acid or unsaturated amidessuch as acrylamide, N-methylolacrylamide or diacetoneacrylamide,styrene, vinyltoluene, vinyl acetate or acrylonitrile, or mixtures oftwo or more of said compounds.

The polymers are prepared by conventional methods of polymer chemistry;for example, by peroxide initiated solution polymerization, emulsionpolymerization or suspension polymerization.

In one preferred embodiment of the invention, component B comprises apolyester, polyacrylate, polymethacrylate, or a mixture of two or morethereof.

Likewise possible for use as component B are polyetherpolyamines orpolyols selected from the group consisting of polyether polyols,polyester polyols, polythioether polyols, polyesteramides, OH-containingpolyacetals and OH-containing aliphatic polycarbonates, or mixtures oftwo or more of said polyols. The hydroxyl number of the polyhydroxycompounds in this case is generally from 15 to 850 mg KOH/g andpreferably from 20 to 600 mg KOH/g.

Suitable polyester polyols, for example, may be prepared from organicdicarboxylic acids having 2 to 12 carbon atoms, preferably fromaliphatic dicarboxylic acids having 4 to 6 carbon atoms, and polyhydricalcohols having 2 to 12 carbon atoms. Examples of suitable dicarboxylicacids are succinic, glutaric, adipic, suberic, azelaic, sebacic,decanedicarboxylic, maleic, fumaric, phthalic, isophthalic orterephthalic acid or mixtures of two or more thereof. The dicarboxylicacids may also be used in the form of the corresponding dicarboxylicacid derivatives, e.g., as dicarboxylic esters of alcohols having 1 to 4carbon atoms or as dicarboxylic anhydrides.

It is preferred to use mixtures of dicarboxylic acids comprisingsuccinic, glutaric and adipic acid in proportions of, for example, from20 to 35:35 to 50:20 to 32 parts by weight, and especially adipic acid.Examples of polyhydric alcohols are ethanediol, diethylene glycol, 1,2-and 1,3-propanediol, dipropylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerol andtrimethylolpropane. A further possibility is to use polyester polyolsfrom lactones, e.g., from ε-caprolactone, or from hydroxycarboxylicacids, e.g., from ω-hydroxycaproic acid.

To prepare the polyester polyols which may be used as a constituent ofcomponent B, the organic polycarboxylic acids or their derivatives ormixtures comprising both may be polycondensed together with thepolyhydric alcohols, without catalyst or, preferably, in the presence ofesterification catalysts. This judiciously takes place in an atmosphereof inert gas, e.g., nitrogen, helium or argon. The polycondensationtakes place, for example, in the melt at temperatures from about 150 toabout 250° C., preferably from about 180 to about 220° C., operatingunder reduced pressure if desired. The reaction is continued until thedesired acid number is obtained, which is advantageously less than 10,preferably less than 2.

At the abovementioned temperatures, the polycondensation may beconducted, for example, to an acid number of from about 80 to about 30under atmospheric pressure and subsequently under a pressure of lessthan 500 mbar, for example, from 50 to 150 mbar. Examples of suitableesterification catalysts are iron, cadmium, cobalt, lead, zinc,antimony, magnesium, titanium and tin catalysts in the form of metals,metal oxides or metal salts. However, the polycondensation may also beconducted in liquid phase in the presence of diluents and/or entrainers,e.g., benzene, toluene, xylene or chlorobenzene.

To prepare the polyester polyols which may be used as component B, theorganic polycarboxylic acids and/or acid derivatives and polyhydricalcohols are polycondensed advantageously in a molar ratio of from about1:1 to about 1:8, preferably from about 1:1.5 to about 1:2.

The polyester polyols obtained possess, for example, a molecular weight(M_(n)) of from 480 to 10000, preferably from 600 to 5000, and inparticular from 600 to 3000.

Likewise possible for use as polyols are polyether polyols, which may beprepared by known processes: for example, by anionic polymerization ofcyclic ethers with alkali metal hydroxides such as sodium or potassiumhydroxide or with alkali metal alkoxides, e.g., sodium methoxide, sodiumor potassium ethoxide or potassium isopropoxide, as catalysts and withthe addition of at least one starter molecule containing, for example,from about 2 to about 8 reactive hydrogen atoms. Likewise possible foruse are polyether polyols prepared by cationic polymerization of cyclicethers with Lewis acids such as antimony pentachloride, borontrifluoride etherate etc. or bleaching earth as catalysts.

Examples of suitable cyclic ethers are tetrahydrofuran, 1,3-propyleneoxide, 1,2- and 2,3-butylene oxide, styrene oxide, ethylene oxide or1,2-propylene oxide or mixtures of two or more thereof. Examples ofsuitable starter molecules are water, organic dicarboxylic acids such assuccinic acid, adipic acid, phthalic acid or terephthalic acid, and alsoaliphatic and aromatic, optionally N-monoalkyl-, N,N- andN,N′-dialkyl-substituted diamines having 1 to 20 carbon atoms in thealkyl radical. Suitable compounds from the last-mentioned class are, forexample, optionally monoalkyl- or dialkyl-substituted ethylenediamine,diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- and1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4- and2,6-tolylenediamine or 4,4′-, 2,4′- and 2,2′-diaminodiphenylmethane.

Further suitable starter molecules include alkanolamines, e.g.,ethanolamine, N-methyl- and N-ethyl-ethanolamine, dialkanolamines suchas diethanolamine, N-methyl- and N-ethyl-diethanolamine andtrialkanolamines, e.g., triethanolamine, and also ammonia. As startermolecules it is preferred to use polyhydric alcohols such as ethanediol,1,2- and 1,3-propanediol, diethylene glycol, dipropylene glycol,1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane,pentaerythritol, sorbitol and sucrose.

Further polyether polyols suitable for use in component B in accordancewith the invention are polymer modified polyether polyols, preferablygraft polyether polyols, especially those based on styrene oracrylonitrile and prepared by in situ polymerization of acrylonitrile,styrene or, preferably, from mixtures of styrene and acrylonitrile in aweight ratio, for example, of from 90:10 to 10:90, in the abovementionedpolyether polyols in accordance with the details of the German Patents11 394, 12 22 699 (U.S. Pat. Nos. 3,304,273, 3,383,351, 3,523,093), 1152 536 (GB 10 40 452) and 11 52 537 (GB 987 618).

Like the polyester polyols, the polyether polyols may be usedindividually or as mixtures. Furthermore, they may be mixed with thegraft polyether polyols or polyester polyols and also OH-containingpolyesteramides, polyacetals, polycarbonates and/orpolyether-polyamines.

Suitable OH-containing polyacetals include, for example, the compoundspreparable from glycols, such as diethylene glycol, triethylene glycol,4,4′-dihydroxyethoxydiphenyldimethylmethane, hexanediol, andformaldehyde. Suitable polyacetals may also be prepared by polymerizingcyclic acetals.

Suitable OH-containing polycarbonates are those preparable, for example,by reacting polyfunctional alcohols such as 1,3-propanediol,1,4-butanediol or 1,6-hexanediol, diethylene glycol, triethylene glycol,tetraethylene glycol, glycerol, trimethylolpropane, triethylolpropane,pentaerythritol, oligo- or polyglycerol, oligo- or polysaccharides withdiaryl carbonates, e.g., diphenyl carbonate, or phosgene.

The polyesteramides include, for example, the predominantly linearcondensates obtained from polyfunctional, saturated and/or unsaturatedcarboxylic acids and/or their anhydrides and from polyfunctionalsaturated and/or unsaturated amino alcohols or mixtures ofpolyfunctional alcohols and amino alcohols and/or polyamines.

Suitable polyetherpolyamines may be prepared by known methods from theabovementioned polyether polyols. By way of example, mention may be madeof the cyanoalkylation of polyoxyalkylene polyols and subsequenthydrogenation of the resultant nitrile (e.g., U.S. Pat. No. 3,267,050)or the partial or complete amination of polyoxyalkylene polyols withamines or ammonia in the presence of hydrogen and catalysts (e.g., DE 1215 373).

In one preferred embodiment of the invention, the polyurethanes areprepared using, at least in part, polyols whose average number of OHgroups per molecule is four or more. In a further preferred embodiment,the average functionality of component B is more than 10.

In one preferred embodiment of the invention, the viscosity of componentA at 23° C. is more than about 8000 mPas.

Besides components A and B, the composition of the invention maycomprise further additives. These include, for example, furtherpolymeric compounds such as melamine resins, examples beinghexamethoxymethylolmelamine, methylated or butylated melamines ormixtures thereof.

Furthermore, the compositions of the invention may also comprisesolvents and additives.

Examples of suitable solvents are toluene, xylene, cyclohexane, mineraloils or naphtha, ketones such as acetone, methyl ethyl ketone or methylisobutyl ketone, esters such as ethyl acetate, n-butyl acetate orCellosolve acetate, or mixtures of two or more of said solvents.

As additives it is possible for accelerators to be present if desired.The accelerators include, for example, organometallic compounds, such asthe organometallic compounds of tin, zinc or lead. Further additiveswhich may be present are antioxidants. These include, for example,sterically hindered phenols, UV absorbers such as benzotriazoles orbenzophenones.

Moreover, dyes or pigments may be present as additives. These include,for example, titanium dioxide, carbon black, indigo, quinacridones, talcor metallic powder pigments such as aluminum.

Additionally, the compositions of the invention may comprise rheologicaladditives such as hydroxymethylcellulose, hydroxyethylcellulose or ureacompounds or a mixture thereof.

The compositions of the invention contain component A in an amount offrom about 5 to about 95% by weight, based on the overall composition.Component B is present in the compositions of the invention in an amountof from about 95 to about 5% by weight.

The ratio of NCO groups of component A to OH groups of component B ispreferably from about 0.6 to 1.4, in particular from about 0.9 to about1.1.

Solvents or other additives may be present overall in an amount of up toabout 80% by weight, preferably from about 0 to about 70% by weight.

The invention likewise provides for the use of at least onepolyisocyanatoisocyanurate which is essentially free from allophanategroups and has an average NCO functionality of more than 3.5 and aviscosity of from 4000 mPas up to 50000 mPas at from 20° C. to 50° C.,measured with a rotational viscometer in accordance with DIN 53019, toprepare surface coatings having a pendulum hardness of at least 80 s,measured by the König method.

In one preferred embodiment of the use according to the invention, thepolyisocyanatoisocyanurate has a functionality of from 4.0 to 7.0. Goodresults may be obtained, for example, if the polyisocyanatoisocyanuratehas a viscosity of more than 8000 mPas up to 30000 mPas at from 20° C.to 50° C., measured with a rotational viscometer in accordance with DIN53019.

In one preferred embodiment, the surface coatings have an improvedscratch resistance or an improved acid resistance relative to surfacecoatings produced with noninventive polyisocyanates. The scratchresistance and the acid resistance are evaluated in accordance with themethods described in this text. Preferably, the acid resistance of thesurface coatings in accordance with the acid test described below is atleast 25 at 70° C.

The invention is illustrated below by examples.

EXAMPLES

1. Preparation of Component A

Hexamethylene diisocyanate (HDI) was introduced into a reaction vesselunder nitrogen blanketing and heated to 80° C. 400 ppm by weight (basedon diisocyanate) of the catalystN,N,N-trimethyl-N-(2-hydroxypropyl)ammonium 2-ethylhexanoate were added,the mixture was reacted at 80° C. and the reaction was stopped when thecrude product had the NCO content specified in table 1 by adding 400 ppmby weight (based on diisocyanate) of di-2-ethylhexyl phosphate.Subsequently, to remove monomeric HDI, the reaction mixture wasdistilled in a thin film evaporator at an oil temperature of 140° C.under reduced pressure (2.5 mbar). The HDI residual monomer contentthereafter was below 0.3% by weight.

Data on the end products are given in table 1.

TABLE 1 Component A, product data Polyiso- NCO content NOC content Visc.cyanate crude product end product 23° C. Average No. (% by wt.) (% bywt.) (mPas) functionality 1 37.3 21.4  4 630 4.0 2 34.6 20.7  8 100 4.33 34.2 20.5  9 300 4.4 4 32.4 20.0 14 800 4.6 5 32.2 19.8 16 400 4.9 630.7 19.5 23 700 5.1 7 29.0 18.9  2 600 5.8 (30° C.) 8 27.2 18.1 21 6006.5 (40° C.)

2. Preparation of an Acrylate Resin as Component B for a Two-componentClearcoat

525 g of pentyl acetate (isomer mixture) were weighed out into a 41stainless steel reactor equipped with oil heating, internal temperaturemeasurement, reflux condenser, stirrer and two feed vessels and heatedwith constant stirring to 140° C. under nitrogen inert gas blanketing.162 g of an aromatics fraction having a boiling range from 160 to 174°C. and 225 g of tert-butyl perethylhexanoate were weighed out into thefirst feed vessel and mixed. 207 g of ethylhexyl acrylate, 462 g ofethylhexyl methacrylate, 360 g of cyclohexyl methacrylate, 858 g of2-hydroxypropyl methacrylate and 6 g of acrylic acid were weighed outinto the second feed vessel and mixed.

The feed stream from feed vessel 1 was commenced at a solventtemperature in the reactor of 140° C. The feed rate was such that, withuniform metering, the mixture from feed vessel 1 ran into the reactionvessel over the course of 4.75 hours. After a further 15 minutes, thefeed stream from the second feed vessel was commenced. The feed rate wasset so that, with uniform metering, the acrylate mixture took 4.00 hoursto enter the reactor. Throughout the metering period, the temperaturewas held at 140° C. After the end of the feed stream from feed vessel 1,the reaction mixture in the reactor was stirred at 140° C. for twohours. The reaction mixture was subsequently cooled to 80° C. andadjusted with 195 g of pentyl acetate (isomer mixture) to a nonvolatilescontent of 65.1% by weight. The solution obtained had an acid number of6.2 mg KOH/g based on the polymer content, a viscosity of 575 mPas(measured as a 60% strength solution in pentyl acetate using arotational viscometer in accordance with DIN 53019 at 23° C.) and amolar mass (number average) of 3150 g/mol, determined by means of GPCanalysis.

3. Use of Components A and B in 2K Polyurethane Coating Systems

3.1 Stock Coating Material

The following constituents were weighed out into a stirred vessel:

72 parts by weight of the acrylate resin solution prepared in example 2(component B),

0.15 part by weight of a polyether modified polydimethylsiloxane, insolution in 2.85 parts by weight of xylene,

1.5 parts by weight of a substituted hydroxyphenylbenzotriazole with 1.0part by weight of an N-methyl-2,2,6,6-tetramethylpiperid-4-yl ester, insolution in 5.0 parts by weight of methoxypropyl acetate,

6.0 parts by weight of butoxyethyl acetate,

5.5 parts by weight of an aromatics mixture having a boiling range from160 to 174° C.

The mixture was homogenized by stirring for 30 minutes.

3.2 Preparation of a Commercially Customary Polyisocyanate Crosslinker(Comparative Example Using a Comparative Component A)

80 parts by weight of a commercially customary polyisocyanurate based onhexamethylene diisocyanate, having an NCO content of 22.3% by weight anda viscosity at 23° C. of 3100 mPas (comparative component A), weredissolved in 10 parts by weight of butyl acetate and 10 parts by weightof an aromatics mixture having a boiling range from 160 to 174° C.

3.3 Preparation of a Polyisocyanate Crosslinker Using the InventiveComponent A

80 parts by weight of the inventive polyisocyanurate 3 (table 1) weredissolved in 10 parts by weight of butyl acetate and 10 parts by weightof an aromatics mixture having a boiling range from 160 to 174° C.

3.4 Mixture of Stock Coating Material and Polyisocyanate Crosslinker

A short time before application, the stock coating material from example3.1 was mixed firstly in a ratio of 100:30 parts by weight with thesolution of a polyisocyanate crosslinker from example 3.2 and also in aratio of 100:33 parts by weight with the inventive polyisocyanatecrosslinker from example 3.3. The mixtures were adjusted with butylacetate to an efflux viscosity of 28 seconds in the DIN 53211 efflux cupat 20° C.

4. Application

Steel body panels pretreated with commercially customary zinc phosphatesolution and bearing a coat of 20 μm of a commercially customarycationic electrodeposition coating material and, atop that, a coat of 35μm of a commercially customary aqueous surfacer were coated by means ofa pneumatic spray apparatus with an anthracite colored aqueous metallicbasecoat to give a dry film thickness of 14 μm. Following theapplication of the basecoat, the system was dried initially at 80° C.for 10 minutes. Then the two coating mixtures from example 3.4 were eachapplied by means of a pneumatic spray apparatus to the initially driedbasecoat, to give a dry film thickness of from 40 to 43 μm. The coatswere flashed off at room temperature for 5 minutes. The panels were thentreated in a forced air oven at an air temperature of 140° C. for 20minutes. The panels were cooled to room temperature, stored for twohours and then assessed.

5. Assessment

The measurements for the clearcoat of the invention were compared withthose for the comparative example containing the commercially customarycrosslinker:

Inventive Comparative Test method Example example Gloss (%, Gardner,20°) 83 83 Pendulum hardness (seconds, König) 133 128 Gloss followingcondensation test (240 hours 84 81 40° C., 98% RAH) Blisters aftercondensation test m0g0 m0g0 Adhesion after condensation test 1.5 2.0Scratch resistance, sand test* (gloss difference, 18.7 22.1 %) Reflowbehavior at 40° C. (remaining gloss 18.7 17.4 difference, %) Reflow at60° C. (remaining gloss difference, 11.6 11.6 %) Chemical resistance(acid test** rating totals) 50° C. 0 0 60° C. 1 1.5 70° C. 6.5 6.5 80°C. 15.5 24.5 Notes: m = amount g = size

*=Sand Test

In the sand test, the finish surface is coated with sand (20 g of quartzsilver sand, 1.5-2.0 mm). The sand is placed in a PE beaker (with itsbase cut off level) which is attached firmly to the test panel. The testpanels used are the same as those described above. The panel, with thebeaker and sand, is set in shaking movements by means of a motor drive.The movement of the loose sand causes damage to the finish surface (100double strokes in 22 s). Following sand exposure, the test area iscleaned of abraded material, wiped off carefully under a jet of coldwater, and then dried using compressed air. The gloss to DIN 67530 ismeasured before and after damage.

**=Acid Test

The acid test is used to determine the resistance of finish surfaces toacids, alkalis and water droplets. The coating, after baking, issubjected to further temperature loads in a gradient oven (30 min at 40°C., 50° C., 60° C. and 70° C.). Beforehand, the test substances (1%, 10%and 36% strength sulfuric acid; 6% strength sulfurous acid; 10% strengthhydrochloric acid; 5% strength sodium hydroxide solution; DI (deionized)water—1, 2, 3 or 4 drops) are applied in a defined manner using ametering pipette. After the substances have been allowed to act, theyare removed under running water and the damage is assessed visuallyafter 24 h in accordance with a predetermined scale:

Rating Appearance 0 no defect 1 slight marking 2 marking/dulling/nosoftening 3 marking/dulling/color change/softening 4 cracks/incipientetching 5 clearcoat removed

Each individual marking (spot) was evaluated and the result for eachcoating was noted appropriately (e.g., rating totals for onetemperature).

Evaluation

The use of the crosslinker of the invention produced clearcoat surfaceswhich have a significantly improved acid resistance relative to theprior art in combination with a virtually identical reflow behavior. Thescratch resistance was at least comparable to that of the clearcoatproduced using the commercially customary crosslinker. At elevatedtemperatures, however, it far exceeded the scratch resistance of thesurface coatings produced in accordance with the prior art.

We claim:
 1. A composition, comprising: component A: at least onepolyisocyanatoisocyanurate which comprises less than 10% allophanategroups in relation to isocyanurate group and has an average NCOfunctionality of more than 3.5 and a viscosity between 4,000 mPas and50,000 mPas when the at least one polyisocyanatoisocyanurate is at atemperature ranging from 20° C. to 50° C., measured with a rotationalviscometer in accordance with DIN 53019: and component B: at least onecompound containing on average more than 10 functional groups which arereactive toward isocyanates to form urea, urethane, thiourethane oramide.
 2. A composition as claimed in claim 1, wherein component A hasan average functionality of from 4.0 to 7.0.
 3. A composition as claimedin claim 1, wherein component B comprises a polyester, polyacrylate,polymethacrylate or a mixture of two or more thereof.
 4. A compositionas claimed in claim 1, wherein component A has a viscosity at 23° C. ofat least 8000 mPas.
 5. The composition as claimed in claim 1, whereincomponent A has an average functionality of from 4.2 to 6.5.
 6. A methodof preparing surface coatings having a König pendulum hardness of atleast 80 s, comprising contacting at least one composition according toclaim 1 with a surface.
 7. The method as claimed in claim 6, wherein thepolyisocyanatoisocyanurate has a functionality of from 4.0 to 7.0. 8.The method according to claim 6, wherein the polyisocyanatoisocyanuratehas a visocosity of more than 8,000 mPas up to 30,000 mPas, measuredwith a viscometer in accordance with DIN 53019 at a temperature of from20° C. to 50° C.
 9. A process for preparing a composition, comprisingmixing a) at least one polyisocyanatoisocyanurate whose fraction ofallophanate groups is least than 10% in relation to isocyanurate groupsand has an average NCO functionality of more than 3.5 and a viscosity offrom 4,000 mPas up to 50,000 mPas when the at least onepolyisocyanatoisocyanurate is at a temperature ranging from 20° C. to50° C.; and b) at least one compound containing on average more than 10functional groups which are reactive toward isocyanates, with formationof urea, urethane, thiourethane or amide.